This invention is directed to internal combustion engines of the reciprocating type, and is more particularly concerned with reciprocating engines combined with an auxiliary cylinder and piston that is driven by the engine exhaust gases. The invention is directed to the extraction of waste energy in the exhaust gases to increase engine power and efficiency, and to reduce cranking losses.
In any reciprocating heat engine, only a small fraction of the input heat energy is converted into rotational energy. In an internal combustion piston-type engine, whether diesel or gasoline, and whether four-stroke or two-stroke cycle, a large fraction of the energy of the hot combustion gases is discharged in the exhaust gases, and leaves the engine without doing any useful work.
In a typical four-stroke gasoline engine, for example, the piston reciprocates twice and the crank rotates twice for a given cycle of intake-compression-power-exhaust phases for each cylinder. In most multiple cylinder engines, the pistons are paired with two pistons reciprocating up and down together, but at opposite strokes in the cycle. That is, in the example of a two-cylinder in-line engine, piston 1 (in cylinder 1) will be in its intake stroke while piston 2 (in cylinder 2) is in its power stroke. Likewise, piston 1 will be in its compression, power and exhaust strokes when piston 2 is in its exhaust, intake and compression strokes, respectively. The pair of cylinders and pistons has one exhaust phase between them for each crank rotation, i.e., for each time the pair of pistons rises from bottom dead center (BDC) to top dead center (TDC). This means that there is hot exhaust gas leaving the pair of cylinders during each rotation. This gas simply travels through an exhaust manifold, to a pollution control device such as a catalytic converter, then to an exhaust pipe. Exhaust gases go directly from a high pressure to atmospheric pressure, so a muffler has to be placed in line in the exhaust pipe to reduce the engine noise. The muffler itself creates a back pressure that reduces engine efficiency.
In my prior U.S. Pat. No. 4,898,041, Drive Linkage for Reciprocating Engine, which is incorporated by reference herein, I introduced the concept of a twin-shaft, counter-rotating crank construction, which allowed the piston to have more dwell on compression and exhaust than on power and intake, and so the compression forces could be spread out over a crank angle exceeding 180 degrees (e.g., 230°). The power and intake would then take place over a crank angle reduced below 180° (e.g., 130°). This allows more of the combustion energy to be used in turning the crank, and reduces the amount of mechanical torque needed for compressing the fuel-air mixture on the compression stroke. In that arrangement, the combustion and power-exhaust-intake-compression phases take place within the cylinders of the device.
I have now found that this same construction as disclosed in my U.S. Pat. No. 4,898,041 can be employed in a supplemental or secondary cylinder for extracting energy from the hot gases that escape the engine cylinders as exhaust from a pair of cylinders of an internal combustion engine. The secondary cylinder can be coupled to the main engine crank to assist in compression and in turning the main engine crank. The secondary or auxiliary piston and cylinder operate in the fashion of U.S. Pat. No. 4,898,041, where the main internal combustion engine cylinders, pistons, and cranks may employ a standard reciprocating rotary design.